Transferring Windows Mail Contacts to Gmail

I have a BT account added to my windows 7 email program.
All my contact are there
However I am finishing with BT and need to know if I delete my BT email account in windows mail what happens to my contacts?

I have just added a Gmail account into windows mail to now use as my default account and want the contacts there.

Thanks
So if I delete the BT account my contacts, that I use for BT mail, will be available to the Gmail account I just added to Windows Mail in its place?

That link just brings up IE Add ons?

I want to be able to access the Gmail account when I am out and about also
So view it on my nexus 4 and 7
I did try and import my Windows contacts into Gmail as a CSV file
They show up there But when I try to send an email on my nexus the name is not suggested as I type the first letter